Observed Signal · Apr 22, 2026 · Technical Release · Source: https://developer.chrome.com/static/blog/feed.xml · Impact: 4/5 · Sentiment: Neutral
Chrome 148 Enables Structured Clone Extension Messaging
Google announced that starting in Chrome 148, Chrome extensions can opt in to use the structured clone algorithm for message serialization instead of JSON. Developers enable the feature by adding "message_serialization": "structured_clone" to manifest.json. Structured clone lets extensions send complex JavaScript types (e.g., Map, Set, BigInt, Date, File, Blob, Error) directly between extension contexts without manual conversion. The feature is opt-in to preserve backwards compatibility; mismatched serialization formats prevent runtime.sendMessage/runtime.connect communication between extensions. Some types and transfer semantics are unsupported (SharedArrayBuffer and transferable ArrayBuffer transfers); native messaging channels still force JSON. Structured clone ignores custom toJSON() methods, and Chrome will continue to support JSON serialization. Developers are asked to test and report bugs via Chromium's issue tracker.
Technical release from a major platform (Chrome) that changes extension messaging capabilities and interoperability; affects developer workflows and compatibility considerations for extension ecosystems.
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Key Takeaways & Evidence Grounding
- Chrome 148 introduces an opt-in structured clone serialization option for extension messaging.
- Enable structured clone by adding "message_serialization": "structured_clone" to manifest.json.
- Structured clone supports complex types (Map, Set, BigInt, Date, File, Blob, Error) that JSON cannot serialize directly.
- Extensions using different serialization formats (JSON vs structured clone) cannot communicate over runtime.sendMessage or runtime.connect.
- Native messaging channels continue to use JSON; transferable objects like ArrayBuffer are copied and SharedArrayBuffer is unsupported.
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